>When updating RFC 1766 for the ISO 639-2 three-letter codes, you may
>wish also to consider the following modifications, relevant to HTML,
>HTTP, CSS and the WAI (Web Accessibility Initiative):
>
...
>2. Provide codes for language-not-known and for no-language. These
> requirements were raised at recent meetings of W3C's HTML WG and
> CSS WG. They are needed because HTML has adopted the hierarchical
> language tagging model of RFC 2070, eg:

It is needed even without this, for whatever meaning one attaches to the
language attribute, be it spelling, hyphenation, presentation, text to
speach conversion or anything else. But it should not be language-not-known
or no-language, but language-not-specified.

It is applicable both to text which is not in any human language, for
example code, and to text in arcane languages which the software cannot be
expected to handle.